Separator for paper pulp suspensions

ABSTRACT

Separator for paper pulp suspension in which the apparatus has a pressurized housing with a cylindrical screen dividing said housing into an annular outer chamber which encircles a cylindrical inner chamber into which latter by pressure means, including a pump, pulp is forced through said screen and thence out of said housing, said screen being free of round holes capable of passing large round or cubical fiber bundles and comprising a multiplicity of narrow elongated slitlike apertures in the upstream face thereof, each connecting with a wider elongated groove in the downstream face of said screen, the slits passing only thin, small fibers or particles and the apertures combining with the back pressure of foils rotating against the downstream face of the screen, with the venturi shape of the apertures and with the forward pressure of pump to successively create alternate outward jets and inward flow in said slits to free any particles jammed therein by said pumping pressure.

United States Patent [72] Inventor Emil Holz Reutlingen-Betzingen, Germany [21] Apply No 682,717

[22] Filed Oct. 26,1967

[45] Patented June 1, 1971 [7 3] Assignee Herman Finckh Metalltuch-und Maschinenfabrik Reutlingen, Germany [32] Priority Sept. 16, 1964 [3 3 Germany Continuation-impart of application Ser. No. 485,473, Sept. 7, 1965, now abandoned.

[54] SEPARATOR FOR PAPER PULP SUSPENSIONS 5 Claims, 4 Drawing Figs.

[52] 11.8. C1 210/415 [51] B01d2l/06 [50] Field of Search 210/342 12 P mp lle 3/1965 Lamort 6/1966 Salomon et a1.

OTHER REFERENCES Primary Examiner Reuben Friedman Assistant Examiner-T. A. Granger Att0meyWalter Becker ABSTRACT: Separator for paper pulp suspension in which the apparatus has a pressurized housing with a cylindrical screen dividing said housing into an annular outer chamber which encircles a cylindrical inner chamber into which latter by pressure means, including a pump, pulp is forced through said screen and thence out of said housing, said screen being free of round holes capable of passing large round or cubical fiber bundles and comprising a multiplicity of narrow elongated slitlike apertures in the upstream face thereof, each connecting with a wider elongated groove in the downstream face of said screen, the slits passing only thin, small fibers or particles and the apertures combining with the back pressure of foils rotating against the downstream face of the screen, with the venturi shape of the apertures and with the forward pressure of pump to successively create alternate outward jets and inward flow in said slits to free any particles jammed therein by said pumping pressure.

PATENIED Jun 1 1971 SHEET 1 OF 2 'uull Inventor:

PATENTEB JUN 1 WI SHEET 2 [1F 2 SEPARATOR FOR PAPER PULP SUSPENSIONS This is a continuation-in-part application of U.S. Ser. No. 485,473, filed Sept. 7, 1965, entitled: SEPARATOR FOR PAPER PULP SUSPENSIONS and now abandoned.

The present invention relates to a separator for paper pulp suspensions.

Separators for separating or sorting paper pulp suspensions are known according to which the separator has a stationary perforated basket or perforated strainer which is provided with perforations widening in the direction toward the sorted suspension.

It is further known, with arrangements of this type, to provide rotatable cleaning blades which move along that surface of said basket which faces the nonseparated suspension, in other words, that surface where the narrower or upstream ends of the perforations are located. The degree of fineness of the emulsion sorted by systems of this type, however, is limited, so that it has been impossible heretofore, with separators of this type alone, completely to refine paper pulp suspensions for paper production. It was heretofore necessary to employ at least one additional separator or sorter of another type, for instance, a pipe separator or a separator in which the suspension had to pass through very fine longitudinal slots.

It is, therefore, an object of the present invention to provide a separator for paper pulp suspensions, which will overcome the above-mentioned drawbacks.

It is another object of this invention to provide a separator of the above-mentioned general type which will be successful in separating fine paper pulp suspensions which may be used for the production of fine paper.

These and other objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawings, in which:

FIG. 1 is a side view, partly in section, of a separator accord ing to the present invention;

FIG. 2 is a cross section through the separator of FIG. 1, and is indicated by line II-II of FIG. 1;

FIG. 3 is a fragmentary plan sectional view of a portion of the perforated basket and drawn at greatly enlarged scale; and

FIG. 4 is .a view drawn at the same scale as FIG. 3, and looking in at FIG. 3 in the direction of the arrow A.

In the course of test and developmental work directed at the improvement of separators, attempts have been made to make separators of the above-mentioned type having stationary perforated baskets which can be used for the separating of paper pulp suspensions for the production of fine papers. To this end, the baskets have, instead of being provided with flaring holes, been equipped with line widening slots while cleaning blades have been provided arranged to be rotated so as to move along the surface of the basket containing the narrowest ends of the slots. However, these tests and the developmental work were a complete failure with respect to arriving at an improvement in the separator and have, therefore, been abandoned.

Further research directed to discovering new principles for such separators has led to the surprising finding that the fine slots required for the fine separating or sorting necessary for high quality papers can, nevertheless, be successfully used in separators of the above-mentioned type for sorting out of fine paper suspensionsprovided the cleaning blades rotate along that surface of the perforated basket which contains the broader portion of the slots, namely, provided that the said blades rotate in the sorted-out suspension adjacent the wider downstream ends of the slots while, furthermore, the blades perform a cleaning function on the slots.

Based on the above-mentioned finding, the present invention concerns a separator for paper pulp suspensions with a stationary screen basket provided with perforations widening in the direction toward the sorted-out suspension, and is characterized in that the said perforations are designed as longitudinal slots while agitating blades rotate along that surface of said basket which faces the sorted-out suspension.

In connection with the present invention, it has proved particularly advantageous to produce the perforations in the form of slots milled into the basket from the side of the sorted-out suspension in such a way that the widest portion of each opening is located in that surface of the basket which faces the sorted-out suspension while having the contour of a ship, namely, with the said perforation tapering in the form of a keel of a ship from the widest part of the opening into a narrow longitudinal slitlike opening. The slitlike openings may be stamped out so that they will be located within the area of the portion to be milled out.

Referring now to the drawi'ngsin detail, the separator shown in FIGS. 1 and 2 comprises a supporting base portion 10 and a cylindrical main frame or housing portion 11. Main frame portion 11 has a flange lllc by means of which it rests on base portion I0 and is connected thereto in any convenient manner, for instance by bolts. The upper end of main frame portion 11 is provided with a flange lllb to which is connected a cover 16 for closing the upper end of main frame portion 11. The separator according to the invention is, in a manner known per se, provided with means, such as an eye bolt, for facilitating the lifting of cover 16 off the main frame portion 1 1.

Arranged within the interior of main frame portion 11 is a tubular, preferably cylindrical, perforated basket or screen 12 having its ends provided with reinforcing rings 21 and 22 for supporting and centering the basket 12 in the main frame portion 111.

Frame or housing portion 11 has connected thereto an inlet pipe 11g which leads into an annular chamber D confined inside of main frame portion 11, inwardly extending flange 1 1c of main frame portion 11, screen 12, and reinforcing ring 2]. Flange llle has that surface thereof which faces chamber D designed as an annular trough from which suspension can be drained through a pipe connection 11h (FIG. 2).

Flange llle confines an opening 111' through which the inner chamber E confined by screen 12 and cover 16 communicates with the receiving space lobformed by the base portion 10 of the separator. Space 10b has an outlet 10a for withdrawing the suspension from the said space.

Arranged in space 10b of base portion 10 is a bearing 23 which supports a vertical shaft 24. Shaft 24 extends outwardly to beneath space 10b and has connected thereto a pulley 25 over which passes a belt 26 to a pulley 27 connected to the shaft of an electric motor 28. Motor 28 is flanged to the base 10 of the separator.

The upper end of shaft 24 which is disposed inside screen 12 on the axis thereof, has connected thereto two arms 29 and 30 of a cross section which is relatively flat in upright direction. The outer ends of said arms carry cleaning blades or foil 14 and 15 which act as agitators and which rotate with shaft 24 in the direction of the arrow C in FIG. 2. The blades 14 and 15 are so arranged with regard to screen 12 that they pass rather closely along the inner side of screen 12. Moreover, said blades or vanes 14 and 15 are inclined in such a way (see FIGS. 2 and 3) that in response to their rotation in the direction of arrow C, they produce a pressure wave in the direction toward the screen. This pressure wave brings about a back scavenging or rinsing flow in a direction opposite to the direction of flow of the suspension from chamber D through screen 12 into chamber E, and thereby causes a cleaning of the perforations 12a, 12b (FIG. 3) of screen 12.

Perforations 12a, 12b are shown on a considerably enlarged scale in FIGS. 3 and 4. As will be seen from these figures, the said perforations are formed by relatively long and narrow slits at their upstream ends and flaring portions 12b leading to enlarged downstream ends. More specifically, the slot portion 12a is located as a slit in that surface of screen 12 which faces the interior of chamber D, and the portions 12b flare from portions 112a toward that surface of screen 12 which faces the interior of chamber E. As will be seen from FIG. 4, the said flaring portions 12b have at their wider mouth the contour of a ship, so that the flaring portion 12b resembles in shape the outer surface of a ship hull with the slot portion 120 forming the keel thereto. Merely for purposes of example, with a screen 12 having a height of 600 millimeters, the perforations in screen 12 may have a width of 0.4 millimeters and a length of 60 millimeters These perforations are arranged in a plurality of rows one above the other With a screen of the just-mentioned dimensions and perforations, the mouth of portions 12a as located in that surface of screen 12 which faces chamber E may be 2.5 millimeters wide.

It is not necessary that the perforations 12a. 12b extend in vertical direction as shown in FIG. 4, but they may also extend in a different direction, for instance, in the transverse direction or in a direction inclined to the vertical axis of screen 12.

In operation, suspension to be separated is supplied to inlet 11g under pressure to chamber D and passes radially inwardly through perforated basket or screen 12 to chamber E and then to outlet a. Separated out material is conveyed from groove lle via conduit 11h to discharge.

Blades 14 and 15 rotate, as shown in FIG. 2, and agitate the suspension as it is received in chamber E but. in particular, set up a backwash movement of suspension through the openings in basket 12 as each blade passes by a respective opening. This backwash movement dislodges any accumulations at the upstream end of the opening and these accumulations move to the groove lle and are eventually withdrawn from the separator via conduit 11h.

In the described manner, the openings are kept open for the passage of suspension therethrough and can thus be made small enough to yield the high quality suspension needed for fine papers while the separator still maintains a throughput large enough to represent an economically sound operation.

Comparison tests have been conducted, utilizing the arrangement according to the present invention, and arrangements known in the prior art, to verify the rather surprising results obtained from the practice of the present invention.

In these tests, while observing uniform conditions throughout, there were four different systems investigated.

In system la, the basket had holes, round in cross section and widening in the direction of suspension flow therethrough and an agitating mechanism having blades as disclosed in the present application was disposed at the upstream ends of the holes in the basket.

System lb was the same as system la except the agitator was disposed at the downstream ends of the holes in the basket.

In system Ila, the same conditions as set forth for system Ia were observed but instead of round holes tapering outwardly in the direction of suspension flow, the openings were in the form of slots as shown in the present application having narrow slitlike entrance ends and tapering outwardly in the direction of suspension flow to large exit ends.

In system IIb, the same conditions were observed as for system Ila, except the agitator was on the downstream side of the basket instead ofon the upstream side thereof.

Each system was operated under the same conditions with like suspensions.

Useable parameters for evaluating the tests to permit comparison thereof were arrived at as follows:

Yield G," representing the efficiency of the separator with respect to throughput of pulp is arrived at by dividing the sorted pulp by the total pulp and multiplying by 100. This gives a percentage value. Both pulps are calculated as absolutely dry so the moisture content thereofdoes not influence the result.

In respect of the dirt and deposit removed from the pulp as it passes through the separator, this is given by a value S which represents the percentage of reduction of the dirt and deposit component from the unsorted pulp to the sorted pulp.

In arriving at the value S," a measured quantity of unsorted pulp, say 100 g as reduced to an absolutely dry condition, and an equal quantity of sorted pulp were taken. The dirt and deposit component of each was determined and the value S," as a percentage is then given by subtracting the value of the dirt and deposit in the sorted pulp from that of the unsorted pulp, dividing their result by the value of the dirt and deposit component in the unsorted pulp, and multiplying by 100.

It will be appreciated that the best sorting system is that one which maintains the highest values for both (3" and S."

A tabulation of the specific tests conducted is given below:

From the foregoing tabulation, it will be seen that system la is quite poor in respect of dirt and deposit reduction and would not produce pulp suitable for high quality paper.

System lb represents an improvement in both throughput and dirt and deposit reduction but also would not produce a high quality pulp.

System Ila, having slots shows a material improvement in the removal of dirt and deposits but has reduced throughput. It appears that some obstruction of the slots occurs in system Ila which reduces the throughput while, at the same time also retards the movement of dirt and deposits through the slots.

System lIb, representing the structure of the present inven- -tion shows a high G value and a high 5" value and produces pulp suitable for high quality papers. It appears that the backwashing action of the agitator blades dislodges dirt and deposits from the upstream ends of the slots so this component can migrate to the discharge conduit therefore and that no tendency exists for this component to become lodged in the slots or be forced therethrough. Rather, the slots are kept clean for the passage therethrough of suspension and this fact, together with the continuous dislodging of dirt and deposits away from the narrow entrance ends of the slots toward the unsorted suspensions side of the basket result in the high values of G" and 8'' observed in the tests and given in the above table.

It will be evident that the speed of movement of the blades in the circumferential direction of the basket is selected to obtain the backwashing action referred to. For high inlet pressures which produce high rates of flow of suspension through the slots, the speed of the blades would be correspondingly higher than for slower speeds of suspension flow to obtain the said backwashing action.

It will be noted that the perforations 12a, 12b are somewhat of the venturi type, with the flaring portion 12b constituting a relatively wide, elongated, tapered groove terminating at its small end in the relatively narrow, elongated, parallel walled slot 12a, the latter forming a constricted throat. When the influent pressure of the pump P, forcing the pulp forwardly through the line slots 12a for screening, is intermittently counteracted, or overcome, by the back pressure created by the foils 14 and 15, the back pressure exerted in the tapered groove 12b is reduced with a corresponding increase in velocity in a rearward direction back through slots 12a. Any bundles of fibers, foreign material or fibers stapled on the edges of the slots or caught in the slots, are thus impacted by the back jet created, with repeated blows depending on the predetermined speed of rotation of the foils, until dislodged. The trailing portion of the foils probably creates a repeated cycle of forwardly directed pressure in pulses, tending to increase the normal pump pressure and thereby suck stapled fibers through the screen slots or to alternately vibrate any clogged material forwardly and rearwardly until it disintegrates, passes through the slots, or is dislodged from the slots.

It is, of course, to be understood, that the present invention is, by no means, limited to the particular construction shown in the drawings, but also comprises any modifications within the scope of the appended claims.

I claim:

1. In a screening apparatus of the type having a pressurized housing with a perforated cylindrical screen dividing said housing into an annular, outer chamber encircling a cylindrical inner chamber pressure means for forcing pulp into said outer chamber, forwardly through the perforations of said screen into said inner chamber and thence out of said housing; each of the perforations in said screen comprising a slot hav ing a narrow elongated slit in the outer upstream face of said screen and a wide, elongated, outwardly tapered groove connecting with and bordering the sides of said slit on the inner downstream face of said screen, and a plurality of forwardly rotating vanes extending along the downstream face of said screen with the surface of each vane adjacent said screen decreasing in distance from said screen from its leading edge rearwardly, so that the surfaces of each blade and the screen converge from said leading edge and create pressure outwardly through said perforations to clear said slits.

2. in a separator for paper pulp suspensions of the type having a pressurized housing with an upstanding perforated cylindrical screen dividing said housing into an annular outer chamber encircling a cylindrical inner chamber, pressure means for feeding said suspension under pressure into and around said annular outer chamber, through said screen from the outer face to the inner face thereof, and thence out of said inner chamber, said screen having a multiplicity of identical separator slots forming the perforations in said screen, each slot having a fine, narrow, elongated slit in the outer face of said screen widening into a coarse, wide, elongated groove on the inner face of said screen having its sides diverging from said slit, said slits being adapted to bar round or cubical particles wider than said slits, but to pass narrow particles such as fibers through said slots, and a plurality of forwardly rotating foil-shaped vanes extending along the inner face of said screen, each of said vanes having a curved surface adjacent said screen which curves toward said screen from its leading edge to decrease the distance between the surfaces of said vane and screen rearwardly from said leading edge, so that the adjacent surfaces of each vane and the screen converge rearwardly from said leading edge and create pressure outwardly through said perforations to clear said slits.

3. A paper stock separator having an annular, influent, pressure chamber separated from a cylindrical, effluent pressure chamber by an upstanding, perforated, cylindrical screen and having a pressure pump-feeding stock under predetermined pressure from said influent chamber through said screen into said effluent chamber, said separator being characterized by: separator slots forming the perforations in said screen, comprising a multiplicity of identical, equally spaced-apart, fine, narrow, elongated slits in the upstream face of said screen, each slit merging into a coarse, wide, elongated groove with sides diverging from the slit to the downstream side of said screen, and clearance blades extending along said screen and mounted to rotate at a predetermined speed within said effluent pressure chamber in a cylindrical path proximate to, but spaced from, the downstream face of said screen, the surface of each blade proximate to said screen being inclined rearwardly toward said screen from its leading edge to closely adjacent said screen, said blades cooperating with said screen to create pressure through said slots and backwash into said grooves and out of said slits to dislodge any particles of said stock from the upstream face of said screen.

4. A paper stock separator as specified in claim 13 wherein: the groove on the downstream face of each slot is at least five times wider than the slit on the upstream face of said slot and each said slot is at least 25 times the width of said groove in length, whereby if the groove is 2.5 millimeters in width, the slot is about 0.4 millimeters in width and the slot is about 60 millimeters in length. 5. A paper stock separator as specified in claim 3 wherein: each fine narrow slit in the upstream end of each slot is defined by a pair of parallel, elongated sidewalls to define a slit of rectangular configuration and predetermined depth, and each said groove in the downstream end of each said slot is defined mainly by a pair'of diverging, elongated sidewalls to define a boat-shaped configuration of predetermined depth substantially. greater than the depth of said parallel walled slit. 

2. In a separator for paper pulp suspensions of the type having a pressurized housing with an upstanding perforated cylindrical screen dividing said housing into an annular outer chamber encircling a cylindrical inner chamber, pressure means for feeding said suspension under pressure into and around said annular outer chamber, through said screen from the outer face to the inner face thereof, and thence out of said inner chamber, said screen having a multiplicity of idenTical separator slots forming the perforations in said screen, each slot having a fine, narrow, elongated slit in the outer face of said screen widening into a coarse, wide, elongated groove on the inner face of said screen having its sides diverging from said slit, said slits being adapted to bar round or cubical particles wider than said slits, but to pass narrow particles such as fibers through said slots, and a plurality of forwardly rotating foil-shaped vanes extending along the inner face of said screen, each of said vanes having a curved surface adjacent said screen which curves toward said screen from its leading edge to decrease the distance between the surfaces of said vane and screen rearwardly from said leading edge, so that the adjacent surfaces of each vane and the screen converge rearwardly from said leading edge and create pressure outwardly through said perforations to clear said slits.
 3. A paper stock separator having an annular, influent, pressure chamber separated from a cylindrical, effluent pressure chamber by an upstanding, perforated, cylindrical screen and having a pressure pump-feeding stock under predetermined pressure from said influent chamber through said screen into said effluent chamber, said separator being characterized by: separator slots forming the perforations in said screen, comprising a multiplicity of identical, equally spaced-apart, fine, narrow, elongated slits in the upstream face of said screen, each slit merging into a coarse, wide, elongated groove with sides diverging from the slit to the downstream side of said screen, and clearance blades extending along said screen and mounted to rotate at a predetermined speed within said effluent pressure chamber in a cylindrical path proximate to, but spaced from, the downstream face of said screen, the surface of each blade proximate to said screen being inclined rearwardly toward said screen from its leading edge to closely adjacent said screen, said blades cooperating with said screen to create pressure through said slots and backwash into said grooves and out of said slits to dislodge any particles of said stock from the upstream face of said screen.
 4. A paper stock separator as specified in claim 13 wherein: the groove on the downstream face of each slot is at least five times wider than the slit on the upstream face of said slot and each said slot is at least 25 times the width of said groove in length, whereby if the groove is 2.5 millimeters in width, the slot is about 0.4 millimeters in width and the slot is about 60 millimeters in length.
 5. A paper stock separator as specified in claim 3 wherein: each fine narrow slit in the upstream end of each slot is defined by a pair of parallel, elongated sidewalls to define a slit of rectangular configuration and predetermined depth, and each said groove in the downstream end of each said slot is defined mainly by a pair of diverging, elongated sidewalls to define a boat-shaped configuration of predetermined depth substantially greater than the depth of said parallel walled slit. 